Conventionally, the cooling of the various mechanical and electronic parts of an alternator (in particular the bearings, windings, regulating components and rectifiers) is achieved with the aid of one or more ventilating fans which rotate with the rotor and which cooperate with air inlet or outlet apertures formed in the two-part casing, or housing, of the alternator. These apertures, or ports, are generally formed around a front first casing component or front end plate, containing the front rotor bearing and located on the same side of the alternator as the drive pulley, and the second casing component which includes the rear end plate of the casing, containing the rear rotor bearing and located on the other side of the machine. The regulating and rectifying components are carried generally by the rear end plate.
For this purpose, many types of fans, both internal and external, axial or centrifugal, and various combinations of the latter, have been known for very many years. However, it is well known that these fans make a significant contribution to the cost and the axial size of the machine, and that they are somewhat noisy in operation.
For these reasons, attempts have in the past been made, in particular by giving a particular form of construction to the rotor, to enable the rotor itself to act as a ventilating fan by setting up a flow of air between the inlet ports and the outlet ports formed in the casing, so as thereby to obtain an alternator which is less expensive and more compact, and which is more silent in operation. This type of solution, which consists notably in giving the rotor an asymmetrical form, does however have the disadvantage that it leads to substantial increased costs in the design and manufacture of the rotor, while the ventilation effect remains somewhat limited, in spite of everything.